An electrophotographic apparatus can operate at a high speed to give a high printing quality. Thus, it has been used in the field of copying machine, laser beam printer, etc. As the photoreceptor for use in the electrophotographic apparatus, an organic photoreceptor (OPC) comprising an organic photoconductor has been developed and spreaded. The structure of the photoreceptor has changed from a single layer structure having a charge-transfer type complex and a charge generation material dispersed in a binder resin to a laminated structure in which a charge-generating layer and a charge-transporting layer are functionally separated from each other to attain improvements in properties. In its current typical embodiment, this functionally separated type photoreceptor is prepared by forming an undercoating layer on an aluminum substrate, and then forming a charge-generating layer and a charge-transporting layer thereon.
With the progress of technology concerning electrophotographic apparatus, photoreceptors which achieved a high image quality have been required. Since any functional layers such as charge-generating layer, charge-transporting layer and undercoating layer have important effects on electrophotographic properties such as sensitivity, image quality, and stability upon repeated use (repetition stability), attempts have been made to improve these functional layers for the purpose of improving the repetition stability and environmental stability of the photoreceptor.
From this standpoint of view, the inventors made studies of functional layers having a higher sensitivity, image quality and repetition stability. As a result, it was found that a film obtained by drying and curing a compound which undergoes polycondensation upon hydrolysis such as silane coupling agent provides excellent electrophotographic properties as an undercoating layer. Such a knowledge has been put into practical use. The formation of an undercoating layer or interlayer from a compound which undergoes polycondensation upon hydrolysis is disclosed in JP-A-59-22438, JP-A-61-94057, JP-A-2-59767, JP-A-3-18858, JP-A-4-124674, JP-A-4-145416, and JP-A-4-162047. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
These compounds require a proper amount of water to undergo curing reaction. Upon hydrolysis reaction, these compounds undergo dealcoholation of alkoxide groups such as methoxy, ethoxy and butoxy or elimination of chelate groups such as acetyl acetonate, followed by condensation reaction. Therefore, the presence of water content is essential in order to efficiently accelerate the curing reaction of the layer containing those compounds. The water content is normally supplied from water content present in the coating solution, or air during drying to the touch, or air contained in the dryer during drying. Thus, the curing reaction proceeds.
However, the amount of water content present during coating or drying to the touch or in the dryer is not large enough to accelerate the curing reaction. Further, since the amount of water content varies with weather conditions such as seasonal changes of climate, the coat thus obtained can be left insufficiently cured, resulting in fluctuation of layer properties. Therefore, photoreceptor products prepared from these materials show a markedly varied product quality. In particular, films cured in dry winter season tend to show insufficient hydrolytic condensation, and they suffer from defects in electrophotographic properties such as increase of residual potential and imaging failure. On the other hand, if the water content is too much in the coating solution, the hydrolysis reaction undergoes during storage of the coating solution, causing an extremely large change in properties with the lapse of time. Thus, the pot life of the coating solution is drastically reduced.